This application relates to an "anti-Coanda" effect drive, and its use on craft which must perform well at low speeds as well as high speeds. It relates to the placing of a gaseous boundary layer of air between a high velocity stream or layer of water and the hull plate surface and therefor remove in (some measure) its form and area from the resistance. Further, it relates to changing the effective vessel hull form by using the anti-Coanda effect flaps or doors as trim tabs and extendable planing surfaces, and by varying the relationship of the thrust jet stream nozzle area to Corona-Jet gas cavity area, and to vary and selectively relieve suction pressures on the hull (as well as create regions where the hull pressure is raised) in response to a specific operational need. The unit can be used in conjunction with an automated controlling device, such as a computerized control, wherein a specific power-up and power-down sequence can be followed in response to sensor information and specific target parameters that may be achieved as bench marks.
The subject invention deals with anti-Coanda effect boundary layer separation systems. One such hull structure device is an anti-Coanda effect submerged discharging marine jet nozzle propulsion device. Another would be the same device without the jet nozzle located therein, e.g., a pressurized gas cavity or hull "step" useful in establishing a maintainable layer therefrom utilizing the same cavity principles as herein disclosed. Another would be the same devices as above with the flaps or doors useful as extendable trim tabs and planing surfaces, wherein a pressurized gas cavity or hull "step" useful in establishing a maintainable gaseous boundary layer therefrom is established. These cavity types could be located adjacent to each other, and could (although not necessarily so) share the same gas source. Further, they could be activated at and over the appropriate vessel speeds (and the streamlining hull closure flap or door deployed to its best position) to optimize the performance criteria then important (either vessel slowing down or stopping . . . or toward the best transportation efficiency), or in maintaining stability (yaw, pitch, and roll) in a seaway.
The subject invention deals with the anti-Coanda boundary layer separation system used over a broad speed range, wherein the application of the system can be seen to be useful both as a simple drive for displacement craft, in application on variable geometry displacement/planing craft, and on hydrofoil craft wherein the jet performance of a submerged anti-Coanda effect jet is acceptable in coming up to vessel foil lifting speed. Further, the subject invention deals with performance improvements resulting from the placing of the marine jet propulsion system low in the vessel with respect to the water line, and its implications on specialized high speed craft (such as hydrofoil craft, wherein performance losses can be reduced by reducing the pump suction lift, hydraulic head, and lowering the jet nozzle thrust application point toward the hydrofoil centerline of hydraulic drag). Potential, therefore, exists to substantially reduce pump suction and pressure head losses (and deliver the change as improved thrust) and vessel hull resistance (either as foil born and or hull born craft), and thereby increase vessel speed for the amount of power applied.
The subject invention deals with both displacement water craft, and water craft which can be made to perform with good efficiency as both displacement and planing craft (a variable geometry stepped hull can be created depending on "door" location and deployment-at-speed sequencing).
The subject invention deals also with flap or door closure logic, wherein the magnitude and direction of the jet applied thrust may be changed at the point of discharge, and the hull resistance varied at speed, by changing the geometry of the jet discharge (vary jet stream velocity) and the opening size of the Corona air chamber (vary the air supply pressure and the region of hull boundary layer influence). Further, the point at which the thrust can be applied can be controlled through door closure logic, and to the degree (or angle) to which the doors are deployed (and potentially trim influenced), the performance of the vessel optimized through the use of appropriate feedback instrumentation.
Inboard auxiliary or main drive engines which use directed water for propulsive power, such as propellers and marine jets, develop thrust by the transfer of momentum, e.g., the ejection of water away from the boat system. With propeller drives and submarine discharging jets located submerged near the hull, the ejected water drags other water with it and influences the water flow about the hull. This "dragging" of water into a changed path about the hull takes applied thrust away from that available for driving the hull forward. A negative pressure zone of influence is created against the hull, and this in measure cancels a portion of the thrust capability of the propulsive device. Further, by virtue of the propeller or jet nozzle angle and its location, this can affect the direction of applied thrust, the amount of thrust applied in the direction of interest, and the trim of the vessel (and the power lost) in correcting for the thrust application point and direction by foil means (rudder, trim tab, flap, hydrofoil, another driving source, or similar devices).
Further, the unit may be useful on "Flying Boat" aircraft, wherein the aircraft has a hull which is a vessel that must operate efficiently at both displacement and planing speeds. Further, it can be used on hulls which operate above as well as in the water, such as hydrofoil craft. Further, it can be used on submerged hull type craft, such as SWATH (Small Water Plane Twin Hull), "wave piercing" craft, and fully submersible craft.
The propensity for a moving fluid to follow a curved surface it is flowing against is known as the "Coanda Effect". Coanda effect can also be observed on a local or micro level with a flat plate, wherein the fluid couple or attachment between the plate and a moving parallel fluid will be locally disrupted into a curved path. This local disruption in an otherwise ordered flow path is transferable to adjacent streamlines at a rate dependant on the degree of inter streamline couple (e.g., a curved or vortexing path adjacent to the hull plate of a moving vessel). To create an anti-Coanda device, therefor, is to create a means to work against the inter plate and inter fluid streamline couple.
Thrust lost through a propeller or water pumping device as compared with its test tank "model" test is composed of changes (powered vs. unpowered vessel) in a) flow fields of the water pumping device due to installation in the vessel, b) modification of the vessels frictional and eddy drag characteristics due to the water pumping devices changes in the vessels boundary layer flow path at speed, c) modification of the vessels wave making, and d) Coanda effect losses. The total of these losses is called the "thrust deduction factor", or TDF. Simply stated, the thrust fraction (t) lost is the difference between the thrust required to free tow an unpowered vessel at speed as apposed to the shaft thrust required to push the vessel with the propulsor installed. The thrust fraction lost can range from a loss of a few percent to over 50 percent depending on the propulsor and the installation. TDF can be measured by subtracting the VESSEL ENGINED MEASURED THRUST (VEMT) from the IDEAL FREE UNPOWERED VESSEL TOW THRUST (IFUT) or vessel system model tow thrust, and dividing this by the IFUT. This fraction, representing thrust CONSERVED, must be subtracted from 1 and multiplied by 100 to yield percent loss, e.g.,: EQU T percent loss=1-{[(IFUT-VEMT)/IFST]-1}.times.100
The remaining thrust, or actual propulsive thrust, acts to drive the hull into equilibrium with hull resistance as the vessel accelerates to speed. The above assumes a high order of correlation between "model tests" and historical sea trials data. Ideally, IFUT is from a full scale model test.
The total thrust required to drive a vessel at speed, e.g., Thrust Horsepower (THP) is equal to the shaft thrust required to overcome the unpowered Ships resistance at speed (Sr). The NET horsepower driving the vessel is the EFFECTIVE horsepower, or EHP. More accurately defined, EQU THP={T.times.[Vk(l-w)]}/325.6 EQU EHP=[T.times.Vk.times.(l-t)]/326.6 EQU Hp. lost=THP-EHP=(THP).times.t
Where:
T=Propulsor thrust in lbs. PA1 Vk=Speed of ship through water in knots PA1 Va=Propeller speed of advance in knots PA1 t=Thrust Fraction PA1 (1-t)=Thrust Deduction Factor PA1 w=wake fraction where EQU (Taylor)w=(Vk-Va)/Vk=1-(Va/Vk)
The resistance due to the ships underwater profile is composed of Frictional Resistance, Eddy Current Resistance, and Wave Making resistance. The subject invention operates to reduce thrust deduction factor (TDF). The subject invention operates also to reduce the vessels "free towed" driving thrust requirements by reducing the vessels stern wave making and stern hull resistance (due to local frictional and eddy current) properties. The subject drive not only reduces the influence of propulsion system water flow effects on the hull form, but also can changes the "effective" hull shape under the influence of a fluid flow about the vessel after body.
This requirement in terms of after body shape changes with speed, as the after body plate angle (or shape) and internal buoyancy become progressively more important as the vessel speed is reduced. Similarly, as speed is increased, the after body plate angle requirements change. This can be sensed by sensors and corrections made.
The invention herein described is related primarily to submerged discharging water pumping systems used for powering marine vessels, such as a submerged discharging marine jet pumps. It is also related to providing steps, of variable size, in the hull wherein is contained an air or gas supply manifold. It is also related to connecting the submarine discharging anti-Coanda effect jet and the variable anti-Coanda effect steps together in a cooperative way such as to allow separation of the fluid flow field away from the after body of the vessel hull. It is also related to providing variable pressure or planing surfaces on a hull or hulls.
The subject invention provides a means wherein heat from the motor or engine can be used to provide gases for surrounding the ejected submerged discharging jet stream for providing increased net propulsive thrust. Also, the motor or engine waste or exhausted gases can be vented around the outside of the ejected jet stream and/or for providing a gas flow for relieving the suction on a hull step. Alternately, ambient air may be supplied to produce the gaseous boundary layer surrounding the jet stream and against the submerged surfaces of the vessel hull. Alternately, the gas supply to the subject invention may be supplied by a separate chemical gas generator means or compressed gas supply. The gas supply can be valved (for manual and/or automatic operation) to vary the extent of supply to the Corona air charge region, and hence affect the pressure ratio in that region (see FIG. 23).
The gases provided surrounds the submerged water jet or water stream and flows up against the vessel hull and/or flows with the jet or water stream away from the hull. This develops a barrier layer which expands and provides a low average kinematic viscosity shearing layer around the jet stream and against-the-hull, thus working to reduce the gross propulsion system effort in thrusting the vessel forward (as to be hereinafter further explained), and in acoustically isolating the thrusting system (isolating propulsion system and jet discharge noise). Further, this gaseous boundary layer or shearing layer, besides increasing net propulsive thrust and through the modification of the vessels resistance properties, increases boat speed, it also significantly reduces changes the tonal characteristic and amount of noise transmitted into the water.
At very low speeds, this gaseous boundary layer rises against the curved after body of the hull, and provides an imbalance in the vector field of the hull favorable to the vessels forward movement. As the vessel moves forward faster, the rate at which this gaseous field rises no longer contributes to the forward movement of the vessel, and is useful only in fluid field separation from the hull. The vessel therein looses buoyancy in the wake field in which this flow operates. The submarine discharging jet flap or door is then deployed much like an airplane flap, e.g., to act as an after plane of hydraulic support structure, thereby correcting for adverse vessel trim. As the vessel goes faster yet, the water flow velocity on the hull surface can be fast enough that other doors (ventilated by a gas cavity) can be opened, and progressively other resistive portions of the hull coated with a gaseous layer . . . and the buoyant force reduction corrected for by door or flap deployment. As the vessel goes faster yet, the curved form of the after body has been completely separated from the fluid stream and, by flap angle, corrected for . . . and the hull form thereby becomes a semi-planing or planing hull form.
The change in the vessel balance utilizing the above strategies must be taken into account during vessel and system design. The shift in the vessel center of mass with respect to the center(s) of hull support can also be corrected for by appropriate door deployment. Best results are achieved by proper design and location.
The above drive may be useful in applications requiring a broad vessel operational profile, wherein they must operate slowly and with great quietness and unobtrusiveness (stealth), and must then respond also with periods of great speed (such as in types of hydrofoil passenger craft, fishing craft, police type interdiction craft, and in certain types of warfare operations.
To reduce parasitic hull drag and deterioration of jet efficiency by marine life growing inside the jet pump, and for closing of the jet openings to lower hull resistance when the jet system is not in use (when the jet is a power augmentation or auxiliary power source), streamlining and sealing hull closures are incorporated (wherein the flaps or doors are closed or retracted to hull form). The jet system may be used as an auxiliary or thrust augmentation source on vessels which sail, on military and maritime vessels which have as their main power system a fixed blade or controllable pitch propeller system (and as a prime mover in its own right). The aforementioned system may be used as a propulsion system, as well as a bow thrusting system, or partially as a localized thrusting system or a means for ventilation of a variable hull portion or step.